Motor drive circuit

Abstract

A motor drive circuit operates in a first mode in which the output current flowing to a first output terminal from a second output terminal is increasing or in a second mode in which the output current flowing to the first output terminal from the second output terminal is decayed. In the first mode, a first voltage signal is output from the first signal terminal and the ground voltage output from the second signal terminal and, in the second mode, a ground voltage is output from the first signal terminal and a second voltage signal is output from the second signal terminal. The motor drive circuit compares the signals output from the first and second signal terminals and output comparison results to a control unit for controlling the output current through the motor coil.

What is claimed is: 
     
       1. A motor drive circuit comprising:
 a first output terminal connected to a first end of a motor coil; 
 a second output terminal connected to a second end of the motor coil; 
 an H bridge circuit including: 
 a first switch element having a first end connected to a power supply and a second end connected to the first output terminal, 
 a second switch element having a first end connected to ground and a second end connected to the first output terminal, 
 a third switch element having a first end connected to the power supply and a second end connected to the second output terminal, 
 a fourth switch element having a first end connected to ground and a second end connected to the second output terminal, 
 a PWM control circuit controlling the output current flowing into the motor coil by controlling the first to fourth switch elements; 
 a signal control circuit that is supplied with first and second voltage signals from the first and second output terminals, and outputs the first voltage signal and the second voltage signal in accordance with an operating mode, wherein, in a first operating mode, the first voltage signal is output through a first signal terminal and power supply voltage is output through a second signal terminal; and, in a second operating mode, the power supply voltage is output through the first signal terminal and the second voltage signal is output through the second signal terminal; and 
 an electric current detecting comparator that compares the signal output through the first signal terminal with a first reference voltage and supplies a comparison result signal to the PWM control circuit; and 
 a zero point detecting comparator that compares the signal output through the second signal terminal with a second reference voltage and supplies a comparison result signal to the PWM control circuit, 
 wherein the PWM control circuit controls the first to fourth switch elements based on the comparison result signals. 
 
     
     
       2. The motor drive circuit according to  claim 1 , wherein, in the first operating mode, the output current flowing into the motor coil from the second output terminal toward the first output terminal is increasing and in the second operating mode, the output current flowing into the motor coil from the second output terminal toward the first output terminal is decaying. 
     
     
       3. The motor drive circuit according to  claim 2 , wherein
 the PWM control circuit controls the first to fourth switch elements based on the comparison result signal from the electric current detecting comparator. 
 
     
     
       4. The motor drive circuit according to  claim 2 , wherein
 the PWM control circuit maintains the output current in the first operating mode by controlling the first to fourth switch elements when the first voltage signal is between the ground voltage and the first reference voltage, and 
 the PWM control circuit shifts the output current from the first operating mode to the second operating mode when the first voltage signal reaches the first reference voltage. 
 
     
     
       5. The motor drive circuit according to  claim 1 , wherein
 the PWM control circuit maintains the output current in the first operating mode by controlling the first to fourth switch elements when the second voltage signal is between the power supply voltage and the power supply voltage minus the first reference voltage, and 
 the PWM control circuit shifts the output current from the first operating mode to the second operating mode by controlling the first to fourth switch elements when the second voltage signal reaches the power supply voltage minus the first reference voltage. 
 
     
     
       6. The motor drive circuit according to  claim 5 , wherein
 the PWM control circuit shifts the output current from the second mode to the first mode after a predetermined period of time has passed since the output current was shifted from the first mode to the second mode. 
 
     
     
       7. The motor drive circuit according to  claim 4 , wherein
 the PWM control circuit shifts the output current from the second mode to the first mode after a predetermined period of time has passed since the output current was shifted from the first mode to the second mode. 
 
     
     
       8. The motor drive circuit according to  claim 1 , wherein
 the PWM control circuit operates to turn off the first to fourth switches when the second voltage signal reaches the power supply voltage. 
 
     
     
       9. The motor drive circuit according to  claim 1 , wherein
 the PWM control circuit operates to turn off the first to fourth switches when the first voltage signal reaches the power supply voltage. 
 
     
     
       10. A motor drive circuit comprising:
 an H bridge circuit including a first output terminal connected to one end of a motor coil, a second output terminal connected to the other end of the motor coil, a first switch element having one end connected to a power supply and the other end connected to the first output terminal, a second switch element having one end connected to ground and the other end connected to the first output terminal, a third switch element having one end connected to the power supply and the other end connected to the second output terminal, a fourth switch element having one end connected to the ground and the other connected to the second output terminal; 
 a PWM control circuit controlling an output current flowing into the motor coil based on a first voltage signal at the first output terminal and a second voltage signal at the second output terminal, and whether the output current flowing toward the first output terminal from the second output terminal is increasing or decaying; 
 an electric current detecting comparator that compares the first voltage signal with a first reference voltage and supplies a comparison result signal to the PWM control circuit; and 
 a zero point detecting comparator that compares the second voltage signal with a second reference voltage and supplies a comparison result signal to the PWM control circuit 
 wherein, when the output current is increasing, the second voltage signal is output through a first signal terminal and power supply voltage is output through a second signal terminal, and when the output current is decaying, the power supply voltage is output through the first signal terminal and the first voltage signal is output through the second signal terminal, 
 wherein the PWM control circuit controls the first to fourth switch elements based on comparison result signals that are generated based on the first voltage signal output through the first signal terminal and the second voltage signal output through the second signal terminal, and 
 wherein the PWM control circuit shifts the output current between a first operating mode during which the output current is increasing and a second operating mode during which the output current is decreasing by controlling the first to fourth switch elements, the PWM control circuit maintains the output current in the first operating mode when the second signal is between the power supply voltage and the power supply voltage minus the first reference voltage, and the PWM control circuit shifts the output current from the first operating mode to the second operating mode when the second signal reaches the power supply voltage minus the first reference voltage. 
 
     
     
       11. The motor drive circuit according to  claim 10 , wherein
 the PWM control circuit shifts the output current from the second operating mode to the first operating mode after a predetermined amount of time has elapsed since the output current shifted from the first mode to the second mode. 
 
     
     
       12. The motor drive circuit according to  claim 10 , wherein
 the PWM control circuit turns off the first to fourth switches when the second signal reaches the power supply voltage. 
 
     
     
       13. The motor drive circuit according to  claim 10 , wherein
 the PWM control circuit turns off the first to fourth switches when the first signal reaches the power supply voltage. 
 
     
     
       14. A motor drive circuit comprising:
 an H bridge circuit including first and second output terminals on either side of a motor coil and a plurality of switch elements, and connected to a power supply; 
 a signal control circuit configured to receive first and second input signals from the H bridge circuit and output first and second output signals through first and second signal terminals, respectively, based on whether an output current flowing into the motor coil toward the first output terminal from the second output terminal is increasing or decaying; 
 a first comparator configured to compare a voltage of the first output signal with a voltage of the power supply less a voltage of a first reference signal, and outputting a first comparison signal; 
 a second comparator configured to compare a voltage of the second output signal with a voltage of a second reference signal, and outputting a second comparison signal; and 
 a PWM control circuit configured to control the output current flowing into the motor coil based on whether the output current flowing toward the first output terminal from the second output terminal is increasing or decaying and the first and second comparison signals. 
 
     
     
       15. The motor drive circuit according to  claim 14 , wherein the signal control circuit comprises:
 a first transistor having one end connected to the power supply and another end connected to the first signal terminal, 
 a second transistor having one end connected to the first signal terminal and another end connected to the second output terminal, 
 a third transistor having one end connected to the power supply and another end connected to the second signal terminal, and 
 a fourth transistor having one end connected to the second signal terminal and another end connected to the first output terminal, wherein 
 the signal control circuit controls the first and second transistors to be on/off in a mutually exclusive manner, the third and fourth transistors to be on/off in a mutually exclusive manner, and the first and fourth transistors to be on/off in accordance with a mode signal from the PWM control circuit.